Steerable crawler track

Abstract

A steerable crawler track for an agricultural utility vehicle such as a tractor or a self-propelled harvesting machine has a left-side track roller unit, a right-side track roller unit, a differential having a transmission input driven by an engine, a first transmission output for driving the left track roller unit, and a second transmission output for driving the right track roller unit and a hydraulic transmission having a variable transmission ratio (i). The transmission outputs of the differential are coupled to one another via the hydraulic transmission such that the ratio of the rotational speeds (n l , n r ) of the transmission outputs are influenced by changing the transmission ratio (i) of the hydraulic transmission.

What is claimed is: 
     
       1. A steerable crawler track for an agricultural utility vehicle, comprising:
 a left-side track roller unit; 
 a right-side track roller unit; 
 a differential having a transmission input, which is driven by an engine, a first transmission output coupled to the left-side track roller unit via a first coupling, for driving the left-side track roller unit and a second transmission output coupled to the right-side track roller unit via a second coupling, for driving the right-side track roller unit; 
 a hydraulic transmission having a variable transmission ratio (i), wherein the first and the second transmission outputs of the differential are coupled to one another via the hydraulic transmission such that a ratio of the rotational speeds (n 1 , n r ) of the first and the second transmission outputs is influenced by 
 
       changing the transmission ratio (i) of the hydraulic transmission; and
 a control device for decoupling the transmission outputs from the hydraulic transmission; 
 wherein the first coupling and the second coupling are friction clutches. 
 
     
     
       2. The crawler track according to  claim 1 , wherein the first friction clutch is disposed between the first transmission output and a first member of the hydraulic transmission and the second friction clutch is disposed between the second transmission output and a second member of the hydraulic transmission. 
     
     
       3. The crawler track according to  claim 2 , wherein the first member of the hydraulic transmission embodies a first hydrostatic unit, which can be brought into a drive connection with the first transmission output, and the second member of the hydrostatic transmission embodies a second hydrostatic unit, which can be brought into a drive connection with the second transmission output, and wherein the first and the second hydrostatic units are interconnected within a hydraulic circuit. 
     
     
       4. The crawler track according to  claim 3 , wherein at least one of the first and the second hydrostatic units has a variable intake volume and pump capacity. 
     
     
       5. The crawler track according to  claim 4 , wherein the first and the second hydrostatic units can be brought into a drive connection with the associated first and second transmission outputs via respective spur gear stages. 
     
     
       6. The crawler track according to  claim 5 , wherein each respective spur gear stage includes a first spur gear assigned to one of the first and the second hydrostatic units and a second spur gear, wherein the second spur gear meshes with the first spur gear and wherein the respective second spur gears are assigned to the first and the second transmission outputs, respectively. 
     
     
       7. The crawler track according to  claim 6 , wherein the second spur gears, which are assigned to the first and the second transmission outputs, respectively, are assigned a respective one of the first and the second couplings, and are used to disengage or engage a drive connection between the particular second spur gear and the first and second transmission outputs. 
     
     
       8. The crawler track according to  claim 3 , wherein the hydraulic circuit can be connected to a hydraulic pump that is driven by a drive motor. 
     
     
       9. A steerable crawler track for an agricultural utility vehicle, comprising:
 a left-side track roller unit; 
 a right-side track roller unit; 
 a differential having a transmission input, which is driven by an engine, a first transmission output, coupled to the left-side track roller unit via a first friction clutch, for driving the left-side track roller unit and a second transmission output coupled to the right-side track roller unit via a second friction clutch, for driving the right-side track roller unit; 
 a hydraulic transmission having a variable transmission ratio (i), wherein the first and the second transmission outputs of the differential are coupled to one another via the hydraulic transmission such that a ratio of the rotational speeds (n 1 , n r ) of the first and the second transmission outputs is influenced by changing the transmission ratio (i) of the hydraulic transmission; and 
 a control device operable to decouple the first and the second transmission outputs, via the respective first and second friction clutches, from the hydraulic transmission depending on an operating parameter selected from the group consisting of: a ground speed of the crawler track, a rotational speed of the transmission input, a rotational speed (n 1 , n r ) of one or both of the first and the second transmission outputs, and a rotational speed of one or both of the first and the second hydrostatic units. 
 
     
     
       10. The crawler track according to  claim 9 , wherein the control device is operated to actuate the first and the second friction clutches jointly using a control. 
     
     
       11. A steerable crawler track for an agricultural utility vehicle, comprising:
 a left-side track roller unit; 
 a right-side track roller unit; 
 a differential having a transmission input, which is driven by an engine, a first transmission output for driving the left-side track roller unit and a second transmission output for driving the right-side track roller unit; 
 a hydraulic transmission having a variable transmission ratio (i), wherein the first and the second transmission outputs of the differential are coupled to one another via the hydraulic transmission such that a ratio of the rotational speeds (n 1 , n r ) of the first and the second transmission outputs is influenced by changing the transmission ratio (i) of the hydraulic transmission; and 
 a means for decoupling the transmission outputs from the hydraulic transmission; 
 wherein the crawler track is configured to operate in one of first and second operating modes (M 1 , M 2 ), 
 wherein the first operating mode (M 1 ) is a coupled operating mode in which the first and the second transmission outputs of the differential are coupled to one another via the hydraulic transmission such that the crawler track is steered by changing the transmission ratio (i) of the hydraulic transmission and via an associated change in the ratio of the rotational speeds of the left-side and the right-side track roller units, and 
 wherein the second operating mode (M 2 ) is a decoupled operating mode in which the first and the second transmission outputs of the differential are decoupled from the hydraulic transmission such that, in a forced driving state of the crawler track, the ratio of the rotational speeds (n 1 , n r ) of the first and the second transmission outputs is adapted to the forced driving state. 
 
     
     
       12. The crawler track according to  claim 11 , further comprising a control device that is operated to select one of the first or the second operating modes (M 1 , M 2 ) of the crawler track depending on one or multiple operating parameters selected from the group consisting of: the ground speed of the crawler track, a rotational speed of the transmission input, a rotational speed (n 1 , n r ) of one of the first and the second transmission outputs, and a rotational speed of one or both of the first and the second hydrostatic units. 
     
     
       13. The crawler track according to  claim 11 , wherein the first operating mode (M 1 ) is selected for ground speeds, for rotational speeds (n 1 , n r ) or both, that are below a predefinable value and the second operating mode (M 2 ) is selected for ground speeds, for rotational speeds (n 1 , n r ) or both, above the predefinable value. 
     
     
       14. An agricultural utility vehicle having, a half-track design and a vehicle structure that is supported on the ground by a crawler track as defined by  claim 11 , and by an additional axle, wherein the additional axle is steerable to steer the utility vehicle at least in the second operating mode (M 2 ).